The allotransplantation (Tx) of deceased human donor islets into the portal vein (PV) in patients with type 1 diabetes has been followed by encouraging results. However, there is (i) a significant incidence of morbidity from hemorrhage or thrombosis, and (ii) an immediate loss of a large mass of islets (estimated at 60-80%) through an inflammatory response known as the 'instant blood-mediated inflammatory reaction'(IBMIR). (iii) Biopsy of the site of the islets is not possible, and therefore the cause of loss of islet function, e.g., acute rejection, cannot be fully assessed. The gastric submucosal space (GSMS) offers several potential advantages, which we have explored in a diabetic pig islet Tx model. Even if only equivalent to the PV, the GSMS offers advantages in the form of (i) endoscopic access, (ii) reduced technical complications, and (iii) potential ability to biopsy. After islet Tx into the GSMS, we hypothesize that endoscopic biopsy can provide evidence of allograft rejection, and this will correlate with blood glucose levels and insulin requirements. The specific aim of this proposed study is to determine whether endoscopic biopsy of islet allografts in the GSMS in diabetic pigs can provide histopathological and immunohistochemical information that correlates with clinical information (e.g., blood glucose level, insulin requirement). This information will allow steps to be taken to enhance islet graft survival (e.g., increase in immunosuppressive therapy) and/or be beneficial to the management of the islet graft recipient (e.g., indicate the need for reTx). MHC full-mismatched pig islet Tx will be performed endoscopically into the GSMS in streptozotocin (STZ)-induced diabetic pigs receiving partial (inadequate) (n=4) or full (n=8) immunosuppressive therapy. The islets will be located by endoscopic ultrasonography (EUS) followed by endoscopic submucosal dissection (ESD) and biopsy on days 14 and 28 after islet Tx. We believe that EUS will allow satisfactory localization of the islet mass, and ESD and biopsy will provide islet tissue that can be stained and examined microscopically. This will provide valuable histopathologic information of help in determining the state of the islets and in modifying the immunosuppressive regimen. This study will provide further confirmation of the advantages of the GSMS as a site for islet Tx, and allow consideration of a clinical trial. PUBLIC HEALTH RELEVANCE: This study will explore the technique and success of taking biopsies of pancreatic islets transplanted into the gastric submucosal space (GSMS) in pigs. In this site, using endoscopic ultrasonography followed by endoscopic submucosal dissection, it should prove possible to biopsy the islets safely, which will allow microscopic examination to detect rejection and other pathological conditions. As this is not possible when islets are transplanted into the liver (the current approach), the ability to carry out islet biopsies successfully and safely will allow modification of immunosuppressive therapy, and should prove a major advance in maintaining healthy islet transplants long-term - 1 -